Traffic markings convey information to drivers and pedestrians by providing exposed visible, reflective, colored and/or tactile surfaces that serve as indicia. In the past, this function was typically accomplished by painting traffic surfaces. Modern marking materials offer significant advantages over paint by dramatically increasing visibility and/or reflectance, improving durability, and temporarily removable marking options. Examples of modern pavement marking materials include; thermoplastics, pavement marking sheet materials, tapes and raised pavement markers.
Preformed and hot applied thermoplastic materials used as pavement markings or for other indicia possess many advantages compared to paints and other less durable markings. These materials can provide years of service life as opposed to paints and other techniques. Known materials include using high friction aggregates on the surface to improve friction. The surface applied aggregates provide good initial values, however as the surface is worn due to traffic, the skid resistance decreases. After surface layers containing anti-skid materials become worn out, these aggregate materials lose their effectiveness and become slippery because they do not contain high friction particles (of sufficient size to provide good skid properties).
Current thermoplastics include the use of primarily polyamide (PA) and/or ethylene vinyl acetate (EVA) resins which have been shown to be unstable and often disintegrate in the presence of alkaline (pH of 8 or greater) environments. Certain (often newer) concrete compositions can also often become caustic and more highly alkaline in the presence of moisture after precipitation laden weather events. Today's preform thermoplastic materials do not include alkaline resistant properties using copolymers of polypropylene (PP) and polyethylene (PE) resins primarily due to the lack of understanding of the effects of alkalinity on long term durability of these olefin resins. Many of the preformed thermoplastic decorative patterned material compositions currently employed for runway applications deteriorate rapidly in the presence of these alkaline environments.
A review of these issues demonstrates the need for thermoplastic products that provide alkali resistance to marking products for installation on paved airport (and alkaline road) surfaces and also ensures that the integrity of the product (and pattern if so desired) is maintained after installation.
Airport pavement indicia and signs provide information that is useful to a pilot during takeoff, landing, and taxiing. Generally airport indicia are grouped into four categories: runway indicia, taxiway indicia, holding position indicia, and other indicia. Indicia for runways are white. Indicia for taxiways, areas not intended for use by aircraft (closed and hazardous areas), and holding positions (even if they are on a runway) are yellow. Indicia for heliports are white with the exception of medical helicopter areas which are white and include a red cross.
Most of the runway and taxiway information provided today still employs paint onto concrete or asphalt surfaces. This paint may last for several weeks or several months depending on the amount of use, the size of the aircraft traffic using it, and/or the severity of environmental conditions.
It has been found that uniformity in airport indicia and signs from one airport to another enhances safety and improves efficiency. FAA Standards AC 150/5340-1 “Standards for Airport Indicia” and AC 150/5340-18 “Standards for Airport Sign Systems” are both references that define the minimum requirements for airport indicia and signage. Non-maintenance of painted indicia may allow indicia to deteriorate to a point where the information being conveyed is confusing or illegible.
Runway indicia may also be divided into the following groups: visual runway indicia, non-precision instrument indicia and precision instrument indicia. Additional indicia are required for runway lengths over 4000 feet and for runways serving international commercial transports.
Maintenance of the painted surfaces require that runways and taxiways be shut down while the surface is prepared, paint is applied and for required curing time(s). Maintenance of a particular runway may impact the holding and taxiways of adjacent or intersecting pavement. The pavement warnings of adjacent or intersecting pavement must change to denote changes in holding areas, and thresholds to avoid ground collisions with other aircraft.
Presently many airports have allocated budgets for painting the warning, identification and directional indicia. Painting the runway surfaces is performed on a rotational basis which is normally once every three weeks, depending on the volume and size of the aircraft traffic. Although the painting of the runway surface is relatively quick, runway traffic still needs to be rerouted to other runways. This causes flight delays while the painting and drying of the painting occurs. It is also is expensive to continue using these methods in that full time painting crews are continually rotating from runway to runway.
Ground safety remains a problem at busy airports across both the United States and internationally. The movement of aircraft in and around busy airports along taxiways between terminal gates and runways presents numerous opportunities for runway incursions, particularly when visibility is poor. A runway incursion is the entry of an aircraft without clearance onto an active runway from an adjacent ramp or taxiway, for which there is a great deal of risk of collision with a landing or departing aircraft. Incursions are often the inadvertent result of pilot disorientation caused by poor visibility.
Incidents associated with poor or inadequate airport indicia such as taxiway collisions or near misses resulting from vehicle operators mistaking one taxiway for another have occurred. Runway incursions and other taxiway incidents still represent inconvenience and expense even when a ground collision does not result. To return an aircraft to a path from which it has strayed requires a considerable expenditure of time and fuel, and a compromise to the safety of all involved.
In addition to the need for runway signage that is relatively simply and quick to apply and that exhibits exceptional wear characteristics as well as allowing for delayed intervening scheduled maintenance, thereby assisting with the reduction of the cost of maintenance, delayed flights and confusion due to runway rerouting, the signage should also be highly retroreflective and skid resistant.
In addition, the need for high retroreflectivity nighttime visibility has been increased to about 1000 millicandellas/m2/lux (mcd) and this relatively high (with respect to earlier requirements) retroreflectivity requires glass beads that must remain at or near the top surface of the signage to ensure that the retroreflectivity is maintained during and after installation. To create the proper composition of the polypropylene/ethylene (PP/PE) copolymer-based preformed thermoplastic compositions that meet all of these requirements has been a recent challenge and below are listed some embodiments of the present disclosure.